1. Technical Field
The present invention relates to an optical module for an atomic oscillator and an atomic oscillator.
2. Related Art
In recent years, an atomic oscillator using CPT (Coherent Population Trapping) as one of quantum interference effects is proposed, and miniaturization of an apparatus and reduction in power consumption are expected. The atomic oscillator using the CPT is an oscillator using a phenomenon (EIT phenomenon: Electromagnetically Induced Transparency) in which when coherent light having two different kinds of wavelengths (frequencies) are irradiated to an alkali metal atom, absorption of the coherent light is stopped.
In the atomic oscillator, in general, the alkali metal atom such as rubidium or cesium is enclosed in a container (gas cell) made of silicon oxide or the like, and the coherent light is irradiated to the gas cell so that the EIT phenomenon occurs. In the gas cell, the alkali metal atom is gaseous (in the form of gas). In the atomic oscillator as stated above, in order to prevent the change of atomic density in the gas cell, control is performed so that the temperature of the gas cell becomes constant (see, for example, JP-A-2007-336136).
However, in the gas cell as stated above, the respective alkali metal atoms constituting the alkali metal atom gas move in random directions. Accordingly, the respective alkali metal atoms constituting the alkali metal atom gas have a distribution of velocity components in the same direction as the traveling direction of the coherent light. If the alkali metal atoms have the distribution of velocity components in the same direction as the traveling direction of the coherent light, a distribution of apparent wavelengths (frequencies) of the coherent light, that is, wavelengths (frequencies) of the coherent light when viewed from the alkali metal atom is generated by the light Doppler effect (Doppler shift). By this, the line width (light absorption width) of an obtained EIT signal becomes wide, and the frequency accuracy may be reduced.